OK, First of all, I would look at a Tri-Fuel generator, or a Tri-Fuel kit. It will run either from its own gas tank, your NG or PG. So you could keep a PG tank around (or if you have a house pig, good to go), keep some stabilized gas around and run a NG line to somewhere close by your generator point (outside). So you either have NG or PG if available and as a backup, gasoline. Whole house units don't have this option, nor can you lend your whole house unit to a relative or friend whom may be without power when you are not.

We have a NG line that goes into our garage and there is a small hole in our siding we can feed a flexible NG line out to a waiting generator, then we have like a dryer outlet, you could turn off your main panel, plug into the service through this outlet and flip the breaker on this outlet and have a NG running our home. Although I would recommend having an electrician install a transfer switch, as he or she can wire exactly what you want available to run on the generator and makes it a whole lot easier.

The thing is, you need to keep this out of your house/garage (you'd be surprised) and most of the time portables are not weather proof, so you need to keep this in mind, also people like to steal them.

I would chain any generator either to two in ground twist stakes and or your house, of course chains can be cut, so maybe even a cheap motion alarm aimed right at it would help too.